1. Field of the Invention
The present invention relates to an image forming apparatus, a method, and a computer-readable recording medium for detecting position deviation.
2. Description of the Related Art
An image forming apparatus that uses an electrophotography method (e.g., wide format copier, wide format printer) is equipped with an optical writing apparatus including an array of inexpensive light emitting devices (light emitting device array) having a width equivalent to the width of A3 or A4 paper. For example, the optical writing apparatus may include plural LED (Light Emitting Diode) printer heads having plural LEDs and being arranged in a zigzag manner with respect to the main scanning direction, so that writing can be performed on a wide area.
However, with the optical writing apparatus having plural LED printer heads arranged in the main scanning direction, dots formed at a boundary area between adjacent LED printer heads may deviate depending on the precision or the error in which the LED printer heads are positioned or the thermal expansion of the LED printer heads. The deviation of dots results in the generation of undesired black lines or white lines. Thereby, image quality is degraded.
In order to prevent the degrading of image quality, Japanese Patent No. 4019654 discloses an image forming apparatus that uses a sensor to detect the amount of position deviation at the boundary area of adjacent LED printer heads and corrects the position deviation.
With this image forming apparatus, position deviation of LED printer heads is detected by using a PSD (Position Sensitive Detector) sensor that receives light directly from the LED printer heads and referring to the output level of the PSD sensor with respect to the illuminating order and the light quantity of LEDs of the LED printer heads.
However, in order to detect position deviation using this image forming apparatus, it is necessary to position the PSD sensor between a printer head and a photoconductor drum or to provide a light guiding member for guiding light from a printer head to the PSD sensor. However, positioning the PSD sensor between the printer head and the photoconductor drum is extremely difficult because the focal distance of the printer head (space between the printer head and the photoconductor drum) is approximately 2 mm. Moreover, providing the light guiding member increases the size of the image forming apparatus, complicates the configuration of the image forming apparatus, and increases manufacturing cost.
Japanese Laid-Open Patent Publication No. 2007-038546 discloses an image forming apparatus having plural LED printer heads arranged in a zigzag manner with respect to the main scanning direction of a photoconductor and arranging density detection sensors at areas in which the LED printer heads are overlapped. The density detection sensors detect the density of a toner image for a single rotation of the photoconductor. According to the detection result of the density detection sensors, the image forming apparatus corrects the position deviation of the focus of each LED printer head by adjusting the light quantity of each LED printer head.
However, this image forming apparatus requires plural density detection sensors to be arranged at the areas in which the LED printer heads are overlapped. This increases manufacturing cost. Moreover, in a case of correcting the position deviation of the focus of each LED printer head, it is difficult to determine the direction of the position deviation.